Methods and system for diagnosing sensors by utilizing an evaporative emissions system

Abstract

Methods and systems are provided for diagnosing sensors in an engine intake by utilizing in an evaporative leak check module pump (ELCM pump). In one example, during engine off conditions, the ELCM pump in an evaporative emission system of the vehicle may be operated in a pressure mode to flow ambient air from the evaporative emissions system to the intake manifold. During humidity sensor diagnostics, the air flow may be used to generate water vapors within the intake manifold, and humidity sensor may be rationalized by monitoring an output of the humidity sensor; and during MAF sensor diagnostics, MAF sensor may be rationalized by monitoring if the MAF sensor output corresponds to a flow rate generated by the ELCM.

The invention claimed is: 
     
       1. A method, comprising:
 during a first condition when an engine is combusting fuel, adjusting engine operation based on an output of a sensor disposed in an intake of the engine; and 
 during a second condition when the engine is off, indicating degradation of the sensor based on an output of the sensor while flowing air from an evaporative emissions system past the sensor. 
 
     
     
       2. The method of  claim 1 , wherein the engine is coupled in a hybrid-electric vehicle, and the method further comprising, during the second condition, flowing air from the evaporative emissions system past the sensor in response to an engine coolant temperature decreasing to a threshold temperature, the threshold temperature based on an intake air temperature. 
     
     
       3. The method of  claim 1 , wherein flowing air from the evaporative emissions system past the sensor includes operating an evaporative leak detection pump in a pressure mode to pump air through a fuel vapor canister coupled to a purge line of the evaporative emission system, the purge line coupled between the fuel vapor canister and the intake of the engine; and wherein flowing air from the evaporative emission system past the sensor further includes opening a canister purge valve disposed in the purge line. 
     
     
       4. The method of  claim 1 , wherein the sensor is an intake manifold humidity sensor, the humidity sensor indicating humidity of the air in the intake of the engine. 
     
     
       5. The method of  claim 4 , wherein flowing air from the evaporative emission system past the sensor further includes operating a heater coupled with the fuel vapor canister, and opening a canister purge valve disposed in a purge line when a pressure of the evaporative emissions system indicated by a pressure sensor disposed within an evaporative leak check module (ELCM) increases above a threshold pressure. 
     
     
       6. The method of  claim 4 , wherein indicating degradation of the sensor based on the output of the sensor includes indicating degradation in response to a difference between a first humidity sensor output before flowing air from the evaporative emissions system past the sensor and a second humidity sensor output while flowing air from the evaporative emissions system past the sensor greater than a threshold difference. 
     
     
       7. The method of  claim 4 , further comprising, during the second condition, flowing air from the evaporative emissions system past the sensor in response to an ambient humidity greater than a threshold humidity, the ambient humidity indicated by one or more of an onboard ambient humidity sensor output and a local ambient humidity information retrieved from a cloud system communicating with an engine controller. 
     
     
       8. The method of  claim 5 , further comprising:
 in response to not indicating degradation, adjusting engine operation based on an output of the humidity sensor; and wherein adjusting engine operation based on the output of the humidity sensor includes adjusting an amount of EGR delivered to the intake when EGR is ON; and 
 in response to indicating engine degradation, during a next engine operation when EGR is ON, adjusting an amount of EGR delivered to the intake independent of the humidity sensor output. 
 
     
     
       9. The method of  claim 1 , wherein the sensor is a mass air flow (MAF) sensor. 
     
     
       10. The method of  claim 9 , wherein flowing air from the evaporative emission system past the sensor further includes opening a canister purge valve disposed in a purge line, an amount of opening of the canister purge valve based on a size of a reference orifice included within an ELCM; and wherein indicating degradation of the sensor based on the output of the sensor includes comparing a first flow rate determined based on an output of the MAF sensor to a second flow rate based on ELCM pump operation, and indicating degradation of the MAF sensor in response to a difference between the second flow rate and the first flow rate greater than a threshold difference. 
     
     
       11. The method of  claim 10 , further comprising, in response to indicating degradation of the MAF sensor, during a subsequent engine operation, adjusting fueling based on an estimated mass air flow, the estimated mass air flow based on an indication from a manifold air pressure sensor, an indication from a throttle position sensor, and an engine speed. 
     
     
       12. The method of  claim 10 , further comprising, in response to not indicating degradation of the MAF sensor, during a subsequent engine operation, adjusting fueling based on the output of the MAF sensor. 
     
     
       13. The method of  claim 1 , further comprising:
 during the first condition, estimating a soot load of a gasoline particulate filter disposed within an exhaust passage; and 
 during the second condition, responsive to the soot load greater than a threshold, activating a particulate filter heating element, flowing air from the evaporative emissions system to the intake, and subsequently flowing air from the intake to the particulate filter via a first cylinder. 
 
     
     
       14. The method of  claim 13 , wherein flowing air from the evaporative emissions system to the intake, and subsequently flowing air from the intake to the particulate filter via a first cylinder includes closing an intake throttle, and adjusting an intake valve of the first cylinder and an exhaust valve of the first cylinder at overlapping open positions. 
     
     
       15. A method, comprising:
 during an engine off period, in response to engine coolant temperature decreasing to a threshold temperature:
 flowing heated and pressurized ambient air from an evaporative emissions system to an intake passage; and 
 indicating degradation of a humidity sensor disposed in the intake passage in response to an output of the humidity sensor not changing by a threshold amount. 
 
 
     
     
       16. The method of  claim 15 , wherein flowing heated and pressurized ambient air from the evaporative emissions system includes operating an evaporative leak detection pump to pump pressurized air into a fuel canister, operating a heater coupled with the fuel canister to heat the pressurized air, and opening a canister purge valve when a pressure indicated by a pressure sensor disposed in the evaporative emissions system reaches a threshold pressure. 
     
     
       17. The method of  claim 15 , further comprising in response to the output of the humidity sensor changing at least by the threshold amount, adjusting exhaust gas recirculation during a subsequent engine operation based on the output of the humidity sensor. 
     
     
       18. A method, comprising:
 during an engine-off condition, responsive to a fuel vapor canister load less than a threshold and an engine coolant temperature within a threshold temperature range of an engine intake air temperature:
 isolating a fuel vapor canister from a fuel tank; 
 coupling the fuel vapor canister to atmosphere via an evaporative leak check module vacuum pump; 
 activating the evaporative leak check module vacuum pump in a conformation to pump atmospheric air into the fuel vapor canister; 
 opening a canister purge valve; 
 opening an air intake throttle; and 
 indicating degradation of a MAF sensor disposed in an intake manifold in response to an output of the MAF sensor being outside of a threshold range. 
 
 
     
     
       19. The method of  claim 18 , further comprising:
 indicating functionality of the MAF sensor responsive to the output of the MAF sensor being within the threshold range; and 
 updating one or more evaporative emissions system testing schedules. 
 
     
     
       20. The method of  claim 18 , further comprising:
 adjusting one or more engine operating parameters based on an estimated mass air flow during a next engine operation responsive to an indication of degradation of the MAF sensor, the estimated mass air flow based on an intake manifold pressure, a throttle position, and an engine speed; 
 wherein the threshold flow range is based on a commanded operating flow rate of the pump; and 
 wherein an amount of opening of the canister purge valve is based on a diameter of a reference orifice within the evaporative leak check module.